A hybrid vehicle includes an internal combustion thermal engine, which transmits torque to the drive wheels by means of a transmission provided with a gearbox, and at least one electric machine which is mechanically coupled to the drive wheels and electrically coupled to a storage system of electric energy. Normally, the storage system of electric energy includes a plurality of electrochemical batteries which are coupled together in series and in parallel.
The arrangement of the storage system in the vehicle may be very complex, particularly in the case of a sporty, high-performance vehicle which has very small interior spaces. In particular, the storage system must be possibly arranged near the electric machine to reduce the length of the electric connection cables (and thus to reduce the weight of the electric cables and the loss of power by Joule effect in the electric cables themselves), must be possibly arranged in position protected from collisions, must be arranged in position sheltered from sources of heat because it cannot withstand high temperatures, and must be arranged so as not to imbalance the vehicle with its considerable weight (in other words, as close to the center of gravity and to the ground as possible to obtain a good dynamic behavior of the vehicle).
In known vehicles, the aforesaid constraints force to arrange the batteries of the storage system in non-optimal positions and in all cases considerably limit the space usable for the batteries of the storage system. Consequently, the electric energy storage capacities of the storage system is limited, and consequently the possibility of using of the electric machine are also reduced.
It has been suggested to arrange the batteries of the storage system at the flatbed which constitutes the bottom wall of the passenger compartments (i.e. to rest the storage system on the flatbed or to insert the storage system in the boxed flatbed). The arrangement of the storage system at the flatbed offers many advantages, because in this manner the storage system is extremely protected from collisions being arranged within the safety cell of the passenger compartment, is relatively close to the electric machine, is arranged in a position which is not subject to overheating and which is easy to cool down, and is arranged very close to the ground in a central position.
However, the useful height for the storage system is low at the flatbed, particularly in the case of a sporty, high-performance vehicle having a very low overall ground clearance. Consequently, in order to be able to arrange the storage system at the flatbed, the batteries of the storage system must necessarily have a very thin overall thickness. Reducing the overall thickness of an automotive electrochemical battery beyond certain limits is problematic, because an electrochemical cell requires the presence of a constant, uniform contact between anode and cathode and the separator interposed between the anode and the cathode in order to work in optimal manner; to obtain such a constant, uniform contact, it is necessary to apply and keep a uniform compression force which pushes the anode and the cathode towards each other, and it is thus necessary to arrange a mechanical clamping element which generates the uniform compression force. The mechanical clamping element has a relatively high thickness, which added to the thickness of the electrochemical cell, determines a relatively high overall thickness of the electrochemical battery which is not compatible with the available vertical space at the flatbed of a sporty, high-performance vehicle.
Patent application JP2004262413A, which is incorporated by reference, describes a storage system for the storage of electric energy for a vehicle with electric propulsion. The storage system includes a series of batteries which are side by side and are arranged on a common support plane; furthermore, the storage system includes a fastening system provided with a single structure which is screwed to the support plane and keeps all the batteries pressed against the support plane.